From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 846B1C388F9 for ; Thu, 19 Nov 2020 11:06:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A75A246F5 for ; Thu, 19 Nov 2020 11:06:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="1bOoK78r" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726682AbgKSLGM (ORCPT ); Thu, 19 Nov 2020 06:06:12 -0500 Received: from mail.kernel.org ([198.145.29.99]:33014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726648AbgKSLGM (ORCPT ); Thu, 19 Nov 2020 06:06:12 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B45DC246EE; Thu, 19 Nov 2020 11:06:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605783970; bh=1olbbRVpFSDdgOVTAb7nOB/GsIqWepxCIAnl/2QcUOY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1bOoK78rMWppAJaCZjoxWoQM+hZk44QoEbwpJXH2UoGsKdR3L8C7Bnoy9diDciCbr lskHGFiMdBgG9dEnf/rpk5/F3ZqVt7HK3sakNJOTCewJ5RdjJBj7SCxUIY8OpU2Uui jy8sydY+NQnzp4aIgIs2Xl1atp6h1m/x7/3+iZnY= Date: Thu, 19 Nov 2020 11:06:04 +0000 From: Will Deacon To: Quentin Perret Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Peter Zijlstra , Morten Rasmussen , Qais Yousef , Suren Baghdasaryan , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: Re: [PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Message-ID: <20201119110603.GB3946@willie-the-truck> References: <20201113093720.21106-1-will@kernel.org> <20201113093720.21106-9-will@kernel.org> <20201119092407.GB2416649@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201119092407.GB2416649@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Nov 19, 2020 at 09:24:07AM +0000, Quentin Perret wrote: > On Friday 13 Nov 2020 at 09:37:13 (+0000), Will Deacon wrote: > > When exec'ing a 32-bit task on a system with mismatched support for > > 32-bit EL0, try to ensure that it starts life on a CPU that can actually > > run it. > > > > Signed-off-by: Will Deacon > > --- > > arch/arm64/kernel/process.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index 1540ab0fbf23..17b94007fed4 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp) > > return sp & ~0xf; > > } > > > > +static void adjust_compat_task_affinity(struct task_struct *p) > > +{ > > + const struct cpumask *mask = system_32bit_el0_cpumask(); > > + > > + if (restrict_cpus_allowed_ptr(p, mask)) > > + set_cpus_allowed_ptr(p, mask); > > My understanding of this call to set_cpus_allowed_ptr() is that you're > mimicking the hotplug vs affinity case behaviour in some ways. That is, > if a task is pinned to a CPU and userspace hotplugs that CPU, then the > kernel will reset the affinity of the task to the remaining online CPUs. Correct. It looks to the 32-bit application like all the 64-bit-only CPUs were hotplugged off at the point of the execve(). > I guess that is a sensible fallback path when userspace gives > contradictory commands to the kernel, but that most certainly deserves a > comment :) Good point, I'll add this: diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index dba94af1b840..687d6acf2f81 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -619,6 +619,16 @@ static void adjust_compat_task_affinity(struct task_struct *p) { const struct cpumask *mask = system_32bit_el0_cpumask(); + /* + * Restrict the CPU affinity mask for a 32-bit task so that it contains + * only the 32-bit-capable subset of its original CPU mask. If this is + * empty, then forcefully override it with the set of all + * 32-bit-capable CPUs that we know about. + * + * From the perspective of the task, this looks similar to what would + * happen if the 64-bit-only CPUs were hot-unplugged at the point of + * execve(). + */ if (restrict_cpus_allowed_ptr(p, mask)) set_cpus_allowed_ptr(p, mask); } Will